1. Field of the Invention
This invention relates to method and apparatus for joining structural components generally and, in particular, to joining first and second structural components when the first component is a tubular type element having an inner wall surface defining an internal duct and an outer wall surface surrounding the internal duct.
2. Description of the Prior Art
There are a number of applications where a tubular type component needs to be joined, connected or otherwise attached to another component. For example, vertical building modules use hollow vertical columns which must have their lower ends connected to a base. Further, in such building application, tubular type components can be used as beams, which again require joining methods and apparatus.
Other applications include building frames or other structures from tubular type elements, such as truck beds or trailers for semi-trailer trucks. If the tubular elements are formed from aluminum, then important weight reductions can be achieved which translate directly into increased payloads and improved profits.
One of the most extensively used of such connections are utility pole assemblies for street and highway lighting, electric wire carriers, and for other vertical standard uses.
These poles may be made from many materials which are suitable for their intended application, e.g. steel, aluminum or other materials. Most are elongated and tubular. Aluminum is very popular because of its light weight and corrosion resistant qualities.
The most common method of attaching a tubular pole is to weld the lower end of the pole to a base plate which is then connected to an anchor structure. However, welding causes a loss of temper and yield strength. Thus, if the yield strength of an aluminum pole is 25,000 psi, welding will decrease the loading capacity by as much as 57 percent. Therefore, it is preferable to mechanically fasten the pole to a base plate to retain the yield strength and loading capacity. Then a lighter pole can be used which will have the same loading capacity as a larger and more expensive pole which has been attached by welding, particularly since the quality of a weld can vary from piece to piece.
The most popular mechanical fastening method is to use a fixed size inner sleeve which the tubular pole fits over. The inner sleeve may be previously attached to a base plate with provisions for attaching the base plate to an anchor means. The problem with this method is in controlling the size tolerance of both the fixed size inner sleeve and the size tolerance of the internal duct of the tubular pole. In order to have a stable connection, the tolerance between the sleeve and the internal duct must be very close. Unfortunately, in the manufacturing process the desired tolerance cannot be maintained without adding considerable expense to the process.
When the inner sleeve is too small, the pole fit is loose and a hinge effect will occur. This not only reduces the initial load capacity, but permits additional reductions in capacity if the pole metal is fatigued with the pole motion as time passes. If the inner sleeve is too large and is jammed into the tube duct, a shear problem may occur. In any event, the stretching of the pole by an oversized inner sleeve will stress the pole, and may actually cause a rupture, hairline crack, or the like.
Since the problems in this general area are most readily apparent in the joining of tubular pole to an anchor base, and since most of the pertinent prior art is related to tubular pole or similar structural components, this invention will be set forth in that context. While the invention is particularly well suited for and advantageously used with tubular poles, it must be kept in mind that protection is sought in all of the applications for this invention, including those discussed above and hereinafter and in which the invention may be used whether specifically discussed herein or not.
U.S. Pat. No. 4,793,111 discloses a method for mechanically securing a pole to a base without using welding, by using a special extrusion to form an extruded tube wall and a plurality of pairs of elongated rib members co-extruded with the wall to form arcuate races. Clamp members are added to form a complete bore. Each of the bores are then threaded. This is a more expensive process than forming a standard, off-the-shelf, tubular pole. In addition, the use of steel bolts threaded into aluminum threads creates another problem because the steel threads are stronger, e.g. 110,00 psi to 25,000 psi. This will probably in time result in weakened aluminum threads and shearing of the anchor base from the pole.
U.S. Pat. No. 3,894,375 discloses a tubular pole base set in concrete to receive a tubular pole. A wedge in the pole base is jammed against the outside of the pole to hold the pole in place in the base. This is not an effective way to retain an aluminum pole, because it places an unequal stress on the more fragile aluminum.
U.S. Pat. No. 2,952,484 discloses a tube connector for joining tubular lamp standards. That is, a vertical tubular pole is joined to a cantilever arm extending from the top of the pole. The tube connector includes a junction tube which has its upper end welded to the inside of the lower end of the cantilever tube. The junction tube is split vertically to enable it to be expanded after insertion into the tubes it is joining.
Two pairs of expansion blocks are spaced apart inside the junction tube and held in the spaced apart position by opposed elongated straps. The straps are each welded to the inside of the junction tube. Each pair of the expansion blocks are independently expandable.
The only connection of the junction tube to the lower end of the cantilever tube is welding, with all of the attendant problems discussed hereinbefore. Moreover, the welding requires an additional assembly step. Further, since the lower portion of the junction tube is not positively joined or connected to the upper end of the vertical tubular pole, slippage between the junction tube and the inside of the vertical tube pole can happen. This occurs as a result of constantly changing wind loads on both the vertical tube and the cantilever tube, with torque loads on all parts of the tube connector constantly changing. Therefore, the expansion bolts which are freely mounted in blind apertures tend to work backwards in the screw threads on the other end, assisted by the pressure of the expansion blocks in trying to return to a position closer together. This allows the junction tube to retract away from the inner wall of the top of the vertical tube causing slippage and a hinging action between the cantilever--junction tube combination and the vertical pole. The hinging movement further aggravates the slippage, and also creates metal fatigue problems. Finally, all the tube connector parts are not secured to each other into a unitary structure after expansion, as the present invention is, to avoid the problems discussed above.
U.S. Pat. No. 3,437,362 also discloses an expanding device for joining tubular elements used for erecting stand assemblies, scaffolding, shelving and the like. As in the just-discussed U.S. Pat. No. 2,952,484, expansion is obtained by advancing a screw with a specially machined forward end, which engages in cam fashion three other parts to expand all four parts away from each other against the inner walls of a tubular member. In the other embodiments, the same camming action in response to screw advancement occurs. Once again, there is no means for securing the expanded members together in their wall contact position into a unitary structure. Therefore, as in the just-discussed patent, torque will eventually cause the advancing screw to retreat and the expanded members to retract and lose inner wall contact and their joining capability. While this structure might be suitable for shelving and the like, it would not be useful for installations with constantly changing loading such as wind loading. Further, this structure does not have any formation for wire passages through the expansion device in those instances where needed.
U.S. Pat. No. 4,318,629 discloses a clamp member that can be advanced by a screw to engage the inner wall of a tubular frame member to bring the opposing inner wall of the frame member against the clamp member support. Once again, there is no provision for securing the clamp mechanism into a unitary structure to maintain its wall engaging contact.
U.S. Pat. No. 3,653,169 discloses a square or rectangular socket extending upwardly from a base to receive a like-shaped hollow column. There are expandable means that fit inside the hollow column to push the column walls out against the sleeve. However, this system depends upon the sleeve being welded to the base, with the attendant problems discussed hereinbefore. Further, there is no way to provide a wire-way passage through the expandable means if the installation requires it. This system would be very expensive to manufacture. Finally, there is no way to secure the expandable means into a unitary structure.
Accordingly, it is an object of this invention to provide an improved method and apparatus for joining a first component, having a passageway formed therein which opens to the exterior of the first component, to a second component. Such first component may be a tubular wall forming an elongated tubular element having an inner wall surface defining an internal duct, and an outer wall surface surrounding the inner wall surface and the internal duct. Such second component may be another structural component, an anchor means or device, a frame structure, a support element, or other element.
It is a further object of this invention to provide an improved method and apparatus for joining such a first component to a second component which utilizes an expandable means for insertion into or nesting in a passageway or duct or the like. The expandable means is then expanded into supporting and engaging contact with the passageway wall or internal duct inner wall, and is secured into a unitary structure in such supporting engaging contact position.
It is a still further object of this invention to provide the method and apparatus described above which utilizes parts which can be easily and inexpensively manufactured, and which can be utilized with less expensive off-the-shelf tubular elements and readily available anchor means.
Other objects, advantages, and features of this invention will become apparent when the following description is taken in conjunction with the accompanying drawings.